One type of a conventional optical fiber gyro comprises a light source of a laser diode for emitting a light signal, a first optical coupler having bar and cross states for light signals to select one or two of output terminals, a polarizer for polarizing light signals and decreasing interference noise of light signals, a second optical coupler having the same function as the first optical coupler, an optical fiber sensing loop for propagating light signals in clockwise and counter clockwise directions, a phase modulator for modulating phases of light signals propagated through the sensing loop, a light receiver of a photodiode for receiving a light signal supplied from the first optical coupler, and a signal processing circuit for processing an electric signal supplied from the light receiver to calculate a rotation angular velocity in accordance with the below equation, EQU .OMEGA.= s/a
where ".OMEGA." is the rotation angular velocity ".psi.s" is a Sagnac phase difference, that is, a phase difference of light signals propagated through the sensing loop in the clockwise and counter clockwise directions, and "a" is defined by the below equation, EQU a=4.pi.R1/.lambda.c
where "R" is the radius of the sensing loop, "1" is the length of the sensing loop, ".lambda." is the wavelength of the light signal and "C" is the velocity of light.
In operation, a light signal is emitted from the light source to be supplied to the first optical coupler, and the light signal is then supplied via the polarizer to the second optical coupler. Thus, the light signal is divided to be propagated through the sensing loop in the clockwise and counter clockwise directions, and then returned to the second optical coupler. The returned light signal is supplied in the opposite direction to the polarizer, and then to the first optical coupler, from which the light signal is supplied to the light receiver. In the light receiver, the light signal is converted to an electric signal which is then processed in the signal processing circuit. Thus, a rotation angular velocity of a rotating member on which the sensing loop is mounted is calculated in the signal processing circuit. In this conventional optical fiber gyro, even if a light source emitting a less linearly polarized light signal is used, a predetermined precision is obtained in detecting the rotation angular velocity, because a polarizer is used.
In the conventional optical fiber gyro, however, there is a disadvantage in that the number of optical parts is large to increase the cost of fabricating the same, and the assembly of the same is difficult due to the number of the optical parts.
For this reason, another type of a conventional optical fiber gyro has been proposed in which a photodiode is integrated with a laser diode, so that the aforementioned first optical coupler is omitted to decrease the number of the optical parts.
However, the aforementioned disadvantage is never overcome in the latter conventional optical fiber gyro, because the decrease of optical parts is not sufficient in number.
Accordingly, it is an object of the invention to provide an optical fiber gyro in which the number of optical parts is decreased to lower the cost of fabricating the same, and to facilitate the assembly of the same.
It is a further object of the invention to provide an optical fiber gyro in which the reliability is increased in accordance with the decrease in number of optical parts.
It is a still further object of the invention to provide an optical fiber gyro in which a low-priced laser diode is used, because means for decreasing interference noise is adopted.
According to the first feature of the invention, an optical fiber gyro, comprises:
a light source for emitting a light signal;
an optical coupler for receiving the light signal to be divided into first and second light signal, and receiving third and fourth light signals to be combined as a combined light signal;
an optical fiber sensing loop having first and second ends, the first and second light signals being optically coupled to the first and second ends of the optical fiber sensing loop to be propagated through the optical fiber sensing loop in clockwise and counter clockwise directions and to be supplied as the third and fourth light signals from the first and second ends;
a light receiver for receiving the combined light signal to be converted into an electric signal, the combined light signal being transmitted through the light source and the light receiver being positioned behind the light source; and
a signal processing circuit for processing the electric signal to provide a rotation angular velocity of a rotating member in accordance with a phase difference of the third and fourth light signals, the rotating member being loaded with the optical fiber sensing loop;
wherein the light source has a difference in attenuation or amplification factor between two light signals of orthogonal polarizations; and
the optical fiber sensing loop is of a polarization plane maintaining optical fiber.
According to the second feature of the invention, an optical fiber gyro, comprises:
a light source for emitting a light signal;
an optical fiber for propagating the light signal to a predetermined position, the optical fiber having a predetermined length;
an optical coupler for receiving the light signal supplied from the optical fiber to be divided into first and second light signals, and receiving third and fourth light signals to be combined as a combined light signal;
an optical fiber sensing loop having first and second ends, the first and second light signals being optically coupled to the first and second ends of the optical fiber sensing loop to be propagated through the optical fiber sensing loop in clockwise and counter clockwise directions and to be supplied as the third and fourth light signals from the first and second ends
a light receiver for receiving the combined light signal supplied from the optical fiber to be converted into an electric signal, the combined light signal being transmitted through the light source, and the light receiver being positioned behind the light source; and
a signal processing circuit for processing the electric signal to provide a rotation angular velocity of a rotating member in accordance with a phase difference of the third and forth light signals, the rotating member being loaded with the optical fiber sensing loop;
wherein the predetermined length of the optical fiber is set to meet a relation in which a distance difference determined by the predetermined length and a phase difference of two orthogonally polarized lights propagated through the optical fiber is greater than an interference distance of the light source; and
the optical fiber and the optical fiber sensing loop are of a polarization plane maintaining optical fiber.